Initial Sheet Thickness Research Articles

Spiral wind-up of vortex sheets

A model of the spiral wind-up of a vortex sheet by the flow induced by a perpendicular vortex is developed, first in the Euler limit of zero viscosity, then taking account of viscous diffusion. The wind-up of a vortex sheet by a propagating vortex pair is also considered; in this case, the vorticity grows exponentially near the two saddle points of the flow in the moving frame of the vortex pair. Estimates are obtained for the maximum vorticity ω m and maximum enstrophy Ω m attained through this process in terms of the wind-up Reynolds number Re and the initial dimensionless sheet thickness δ 0 . This paper is dedicated to Andrew Soward, whose sustained research in Dynamo Theory and Fluid Mechanics has been brilliantly inspiring for more than 50 years. Happy 80th, Andrew!

Lightweighting an automotive fuel tank through formability analysis

For lightweighting automotive sheet metal parts, it is important to use the right grade/material with the minimum possible initial blank thickness in the forming processes. Fuel tank is one of the most critical sheet metal parts in automobiles due to its complex shape and large depth. In this work, a simulation-based approach has been employed to study the feasibility of lightweighting an automotive fuel tank (for two wheelers) by reducing blank thickness and changing steel grade. Formability analysis has been carried out using numerical simulations of a 0.8 mm thick sheet of Extra Deep Drawing (EDD) steel which is being used to manufacture the fuel tanks. Simulations have been performed to find out the minimum initial sheet thickness which can be formed successfully without failure or excessive thinning. From the predictions of formability, thinning, and strain distributions in the formed parts, it has been found that the weight of the part can be reduced by 12.5% by reducing the initial thickness from 0.80 to 0.70 mm. To reduce the thickness further, simulations have also been carried out by changing the grade from EDD steel to Interstitial Free (IF) steel which has superior drawability than EDD steel. It has been found that the blank thickness can be further reduced to 0.65 mm in the case of IF steel which is expected to result in 19.0% reduction in the weight of the component. The predictions have been validated by the actual press trials in the industry with reduced sheet thickness. The predicted strain distribution and thinning in the formed parts have also been validated with the experimental press trails. In addition to the weight reduction, the proposed change in thickness and grade would lead to a reduction of 16.5% and 4.0%, respectively, in the raw material cost of the fuel tank.

Maximum Thinning Rate Prediction of Friction Heat Single-Point Incremental Forming for AZ31B Magnesium Alloy Based on BP Neural Network

The purpose of this project is to build an accurate prediction model for the maximum thinning rate of the truncated cone made of magnesium alloy AZ31B by single-point incremental forming. A truncated cone’s thickness distribution is analyzed using ABAQUS. Orthogonal experiments and supplementary data were performed as training samples within the maximum refinement rate obtained from the finite element (FE) results. Back-propagation (BP) neural network is established by taking into account tool diameter, initial sheet thickness, and forming angle as input responses, and maximum thinning rate as output responses, and nine hidden layers are involved. The results showed that the incidence of process parameters on the maximum thinning rate of the truncated cone is in the order of forming angle, initial thickness of sheet, and diameter of tool from large to small; The correlation coefficient of BP neural network model training [Formula: see text]. The test results and FE results contrast, and the average error rate of the maximum thinning rate is only 0.97%. The results indicate that the model is reliable and accurate for the prediction of incremental forming, and it is a useful reference value.

Determining the influence and correlation for parameters of flexible forming using the random forest method

Single-point incremental forming (SPIF) enables the forming of fix-clamped sheet metal by moving a relatively small geometrically simple tool along the trajectory, producing the desired shape of the final product. Excessive thinning of the sheet results in fracture, determining the limit of formability. This characteristic of the forming process can be improved by upgrading the basic SPIF process to two-step forming, whereby a more even distribution of the sheet thickness can be achieved by pre-bulging with a hemispherical punch. This study focused on analysing the SPIF process and a hybrid two-step forming consisting of sequential bulging and SPIF. The analysis focused on the output parameters of sheet metal thinning and maximum forming force components and was conducted with Abaqus simulation software. An innovative new approach for influence analysis of technological, material and geometrical input parameters and correlation analysis between the mentioned parameters was performed using the random forest (RF) method, which allows the determination of individual parameter influence by analysing tree-shaped models obtained through the training process. The analysis results show a significant influence of the workpiece wall angle and part depth on thinning and initial sheet thickness on values of the forming force components. The results also show a great correlation between the parameters of the bulging depth and the part depth after SPIF and the significant influence of the appropriate choice of the backing plate geometry for the target product geometry.

Experimental Study on Breakup Characteristics of Hollow Cone Spray in Gas Crossflow

Hollow cone spray with a medium spray half-cone angle (in the range of 36°–45°) exposed to a gaseous crossflow is a situation that has been extensively investigated experimentally. In this experiment, flow visualization techniques are employed to examine the initial liquid sheet thickness at the nozzle orifice exit and the sheet breakup process. The dynamics of the primary breakup of the sheet is analyzed based on the observations of the sheet breakup in the near-nozzle region. The experimental results show that the breakup mechanism of the liquid sheet varies greatly depending on liquid centrifugal momentum and aerodynamic force. Four distinct breakup modes are observed, and the breakup regimes are mapped in the parametric space based on the liquid Weber number (84–2175) and the liquid-to-air momentum ratio (22–8455). It is observed that the leeward side of the sheet is dominated by shear oscillation breakup within the range of the liquid-to-air momentum ratio less than 600. The influences of the aerodynamic Weber number on breakup frequency and the number of surface waves observed on the leeward side sheet are discussed by analyzing the spray images. The breakup-regime transition criteria for hollow cone spray in crossflow and the trajectory of spray in crossflow are proposed by employing a multivariable regression method.

Experimental study of the spray characteristics of twin-fluid atomization: Focusing on the annular flow regime

The characteristics of twin-fluid atomization operating in the annular flow regime were studied experimentally under various gas-to-liquid ratios (GLRs) and injection pressures. The macroscopic morphology of the spray was obtained by shadowgraph, while the droplet size and velocity were measured using a phase-Doppler particle analyzer technique. It was found that the spray cone angle increases almost linearly with the GLR, and the axial distance required for droplet coalescence to outweigh the breakup decreases with increasing GLR. The Sauter mean diameter (SMD) first decreases and then increases along the axial direction due to the competition between turbulent breakup and droplet coalescence. The droplet size follows a lognormal distribution; the droplet velocity distribution is closer to a lognormal distribution under large GLRs, while it follows normal distribution with GLR = 3%. Regarding the radial distribution, low GLRs (3% and 5%) lead to a bimodal spatial velocity distribution, while for large GLRs, the droplet velocity decreases monotonically toward the far field. The spray tends to become more stable with increasing GLR and injection pressure Pinj, whereas the SMD increases with increasing Pinj. The underlying atomization mechanism in a twin-fluid injector in the annular flow state can be regarded as the disintegration of the initial liquid sheet by longitudinal Kelvin–Helmholtz instability followed by transverse Rayleigh–Taylor instability, which yields a direct proportionality of the droplet size to the initial liquid sheet thickness ΔL. Subsequently, for high Pinj, the gas core shrinks and ΔL increases, which results in an increased SMD but enhanced atomization efficiency ΔL/SMD.

Tailoring Titanium Sheet Metal Using Laser Metal Deposition to Improve Room Temperature Single-Point Incremental Forming.

Typically, due to their limited formability, elevated temperatures are required in order to achieve complex shapes in titanium alloys. However, there are opportunities for forming such alloys at room temperature using incremental forming processes such as single-point incremental forming (SPIF). SPIF is an innovative metal forming technology which uses a single tool to form sheet parts in place of dedicated dies. SPIFs ability to increase the forming limits of difficult-to-form materials offers an alternative to high temperature processing of titanium. However, sheet thinning during SPIF may encourage the early onset of fracture, compromising in-service performance. An additive step prior to SPIF has been examined to tailor the initial sheet thickness to achieve a homogeneous thickness distribution in the final part. In the present research, laser metal deposition (LMD) was used to locally thicken a commercially pure titanium grade 2 (CP-Ti50A) sheet. Tensile testing was used to examine the mechanical behaviour of the tailored material. In addition, in-situ digital image correlation was used to measure the strain distribution across the surface of the tailored material. The work found that following deposition, isotropic mechanical properties were obtained within the sheet plane in contrast to the anisotropic properties of the as-received material and build height appeared to have little influence on strength. Microstructural analysis showed a change to the material in response to the LMD added thickness, with a heat affected zone (HAZ) at the interface between the added LMD layer and non-transformed substrate material. Grain growth and intragranular misorientation in the added LMD material was observed. SPIF of a LMD tailored preform resulted in improved thickness homogeneity across the formed part, with the downside of early fracture in a high wall angle section of the sheet.

Investigation on tool properties for the production of components with micro textured surfaces

Defined surface micrcotextures offer potential for the friction reduction in elastohydrodynamic contacts and can thus increase the energy efficiency of technical systems. The production of prostheses, where microtextured surfaces can provide anti-bacterial effects is another application area. To manufacture these components economically in large quantities, forming processes are to be aimed at. Since lightweight parts are crucial in most application areas, the forming of sheet metal is the subject of current research. A major aspect of the presented investigation is the behavior of tool materials for the production of such microtextured sheet metal parts. Applying microtextures of varying geometries to the tools is a key challenge. Limitations in the accuracy of electrical discharge machining processes for the fabrication of micro cylinders, prisms and cuboids are therefore analyzed on the high-speed steels 1.3343 and 1.3244. In addition, the tool surfaces are characterized regarding their friction properties with case hardening steel as a contact partner. In this paper, the tool friction is analyzed for the steel 1.7131 (16MnCr5) with an initial sheet thickness of t0 = 2.4 mm, which is often utilized for high-wear applications due to its high strength and toughness. In this context, the friction behavior of the wax-containing lubricant Beruforge 150 DL made for bulk forming processes is compared with zinc-free high-performance lubricants Raziol CLF 65-400 of varying viscosity.

On appropriate Finite Element discretization in simulation of gas-based hot sheet metal forming processes

Gaseous medium is being used for sheet metal forming at elevated temperatures, especially for lightweighting purposes. These processes enable forming of high strength alloys of a wide range of thickness due to low material flow stress as well as improved formability. In these processes, the resulting component properties are an interplay of numerous parameters. Instead of cost and time intensive experiments, FEM aids an effective and economic process optimization and enables a better understanding of the influence of process parameters on the component properties. In the current study, the importance of appropriate discretization of the workpiece within a gas-based hot sheet metal forming process is investigated based on a laboratory scale component. AA6010 sheet metal blanks of different thicknesses are studied numerically and experimentally. Simulations with different types of elements are performed and the evolution of process parameters as well as their influence on the final component thickness are analysed. Different element types resulted in noticeable difference in the simulation results and this difference also varies with the initial sheet thickness. Upon further experimental validation, the suitable element type for workpiece discretization is suggested, which enables practitioners to get reliable results via FE simulation of these processes.

Investigation on tailored blanks in a full forward extrusion process of sheet-bulk metal forming

Due to the ongoing technological development, the demand for geometrically complicated high performance parts with great functional density is increasing. Often, the use of sheet metal is a beneficial approach in manufacturing technology to meet the requirements on components regarding material strength and lightweight construction goals. The forming of therefore required complex sheet metal part geometries with integrated functional elements cause the need for a three dimensional material flow. Sheet-bulk metal forming, characterized by the application of bulk forming operations on sheet metals, is a suitable approach to produce such components. A challenge is the material flow control, resulting in an insufficient die filling of the functional elements. The use of tailored blanks with a defined sheet thickness distribution is an auspicious approach to face this challenge in subsequent forming processes. In the presented work, semi-finished products with a continuous thickness profile manufactured by orbital forming are applied in a full forward extrusion process. By an additional implementation of a heat treatment, the tailored blanks undergo a recrystallization process that causes a softening of the strain hardened material. In this paper, the potential of a heat treatment in the process class of sheet-bulk metal forming is shown by characterizing the geometrical and mechanical properties of the functional components by applying the mild deep drawing steel DC04 with an initial sheet thickness of t0 = 2.0 mm.

Breakup of thin liquid sheets through hole–hole and hole–rim merging

Abstract

Simulation of sheet metal forming processes by presenting a bending-dependent inverse isogeometric methodology

Recently, eliminating the gap between design and formability analysis of sheet metal parts has been studied to simulate sheet metal stamping processes. In this regard, a transfer-based inverse isogeometric formulation has been proposed. This method has various advantages such as solving the governing equations in two-dimensional networks without any concern about the convergence; however, it neglects the bending effect which is a major contributor in die/punch profile radii. The present work aims to consider the bending effects by introducing a bending-dependent inverse isogeometric formulation. The developed model deals with the minimization of potential energy, deformation theory of plasticity, classical plate theory, and considering a yield criterion in stress-resultant space. In addition to all advantages of the transfer-based inverse isogeometric formulation, one major benefit of this study is that the bending effects are included with a slight increase in the computation time. This methodology allows for accurately predicting the effects of changing die/punch profile radii and initial sheet thickness on the formability of the final part by presenting a new material updating process. To assess the credibility of this approach, an experimental setup and forward FEM software have been utilized to form a rectangular box. The results acquired by the developed method and those achieved by experiment and forward FEM reveal acceptable accuracy in the presented model. Also, strains and thicknesses predicted by the developed method, membrane inverse isogeometric model, and forward FEM for nine different values of punch radius to the sheet thickness ratio have been compared. Considering forward FEM as a reference method, the average of calculated error in the presented model for prediction of thickness at the middle of punch radius zone is around half of that in the membrane model. In solving the studied problems, the presented model requires only slightly more computation time (around 2%) than the membrane inverse isogeometric model and much less computation time than forward FEM. Therefore, the presented method is a valuable inverse forming solver especially when the bending effects are significant.

ЗАКОНОМІРНОСТІ ФОРМУВАННЯ ШТУЧНОЇ ОПТИЧНОЇ АНІЗОТРОПІЇ ПОЛІМЕТИЛМЕТАКРИЛАТА ДЛЯ ПОЛЯРИМЕТРИЧНОГО ВИКОРИСТАННЯ

General principles of wav plate manufacturing are considered. The possibility of the formation of synthetic optical anisotropy of polymethyl methacrylate (PMMA) by the method of its uniaxial stretching is investigated. The most promising is a method for manufacturing waveplates, which includes the stage of controlled stretching of the polymer material to the required phase shift value, which would generally exclude the stage of machining the plates. The general orderliness of the molecules in the polymer resulting from stretching (orientation) leads to the oriented state of the polymer, and, consequently, to the general anisotropy of the physical and optical properties. In this state, a clearly pronounced uniaxial orientation of polymer chains is observed. As a result, chain macromolecules, randomly (statistically) oriented in the initial PMMA, acquire orientation under the influence of an external directed tensile force. The anisotropy of the optical properties of uniaxially stretched PMMA is manifested in the fact that it has different refractive indices for light polarized parallel to the direction of stretching (orientation) and in the perpendicular direction (birefringence). The regularities of the formation of the synthetic optical anisotropy of PMMA have been studied. The dependences of the birefringence values of uniaxially stretched PMMA on the initial sheet thickness, stretching temperature, and degree of stretching have been measured. It has been shown that the value of birefringence is directly proportional to the thickness of the initial sheet and the degree of stretching and inversely proportional to the stretching temperature. The spectral dependence of the birefringence value is measured. Achromatic and superachromatic waveplates were made from uniaxially stretched PMMA. The spectral characteristics of the phase shift of the manufactured waveplates are given. The availability of the starting material, the technological simplicity of the formation of the initial components for waveplates, as well as the possibility of manufacturing waveplates of large dimensions and high quality, make polymethyl methacrylate with artificially induced anisotropy a promising material for the manufacture of achromatic and superachromatic waveplates.

An Investigation of the Effects of a Sheet Material Type and Thickness Selection on Formability in the Production of the Engine Oil Pan with the Deep Drawing Method

In internal combustion engines, in a way integrated under the engine block, the oil pan is used to store the engine oil, to separate foreign substances in the oil coming from the engine block, to lubricate the moving parts, to help the engine cooling system. In this study, by using different materials such as DC06 (IF), AISI 304, Al6082, and DC01 and selecting different thicknesses such as 1.5 mm and 2 mm, the deep drawing method was applied to them, and their formability behaviors with deep drawing were investigated. The effects of the sheet material type and thickness parameters on the tensile force and wall thickness variation on a sample engine oil pan formed by deep drawing were determined. Different parameters were determined for the sample engine oil pan. According to the analysis results, it was detected that the wall thicknesses of the sensitive points were determined to decrease by 0.86 mm, 0.62 mm, and 0.37 mm, respectively, for deep drawn samples with a 1.5 mm thickness (AISI 304, DC06, DC01), but tearing occurred in the Al6082 material. On the other hand, when the sheet material thickness was increased to 2 mm, it was observed that the thickness change rates decreased by 13% in DC06, 0.7% in AISI 304, 33% in Al 6082, and 4% in the DC01 material type in comparison with the initial sheet thickness of 1.5 mm. The results of the analysis obtained in this study demonstrated that these four materials had superiorities over each other, that the thickness of the material was an essential criterion in deep drawing, and that the use of a 2 mm thick AISI 304 material among the selected materials in the production of the engine oil pan was more suitable.

Investigation of coil-break formation during uncoiling of fully annealed low carbon steel sheet using FE simulation

A 3D finite element (FE) model is developed for evaluating the formation of coil breaks during uncoiling of full-annealed low carbon steel sheets. The model consists of a 2-lap coil measuring 600 mm in inner core diameter and 300 mm in coil width with an initial sheet thickness of 1.5 mm. The forward coil tension TF is increased from 31 N/mm to 176 N/mm, and the change in true strains (LE11) and stress distributions (S11) along the longitudinal direction on the top surface of the sheets is recorded. The simulation results showed that there are six highly concentrated LE11 zones i.e. zones A (narrow bands of tensile strains or coil break) and B (islands of compressive strains) formed across the top surface of the sheet. The periodical elastic–plastic deformation is evidenced by the formation of both zones resulting from the localised plastic deformation and the incomplete unbending. The LE11 distribution is uneven across each zone. Although tensile LE11 is obtained in both the middle and edge portions of zones A, the values are compressive in the middle and tensile in the edge portions of zones B. The overall strain value of the sheets increased with increasing TF resulting in decrease in tensile LE11 peak heights in zones A and increase in strain difference between the middle and the edge portions in zones B. The degree of coil-break became more severe with increase in LE11 peak heights as demonstrated in the edge portion of zones B with increase in TF. In the sensitivity analysis using a refined mesh model for TF = 166 N/mm, only the strain values in the edge portions of zones B increased due to the increase in amount of edge curling resulting from the transverse contraction of the sheet under the high TF. With an Anti-Coil-Break (ACB) roll, the amount of edge curling reduced and the amount of tensile LE11 in the edge portions of zones B is successfully reduced by 30%. However, ACB failed to decrease LE11 peak heights in other zones despite using higher applied load.

Effect of process parameters on micro flexible deep drawing of stainless steel 304 cups utilizing floating ring: Simulation and experiments

Due to its simplicity, versatility of process and feasibility of prototyping, using flexible tools in sheet forming seems appropriate for producing cups at microscales. This article presents a novel micro deep drawing technique in which a cooperation of a floating ring, as a primary rigid die, with a rubber pad, as a main flexible die, is employed for forming micro-cups. The function of the floating ring is to overcome minor wrinkles that commonly occur at flange portion, while the flexible die is to complete the forming stroke. The influence of initial sheet thickness, drawing ratio, punch corner radius and rubber height is studied through simulations and experiments. Furthermore, three size scales are adopted to investigate the possibility of using the proposed technique under different process dimensions. The code ABAQUS/Standard is utilized to build the finite element models and thereafter micro-forming experiments are carried out to verify the numerical results. For this purpose, a special setup is developed to be compatible with simulation models. The results show that the formed cups are characterized by very accurate dimensions, high surface quality, homogeneous wall thickness distribution in terms of maximum thinning and thickening and relatively large aspect ratio.

Numerical Investigation of the Influence of some Parameters in SPIF Process on the Forming Forces and Thickness Distributions of a Bimetallic Sheet CP-Titanium/Low-carbon Steel Compared to an Individual Layer

The single point incremental forming process (SPIF) of sheet metal is an emerging manufacturing process which still in progress. It is well-known to be perfectly suited for prototyping and small series. However, this process is not really industrialized yet, mainly due its geometrical inaccuracy, its non-homogeneous thickness distribution... Moreover, considerable forces can occur. They must be controlled in order to preserve the tooling. For this purpose, many different research studies were conducted in order to investigate its different aspects. The application of single point incremental forming to bimetallic composite sheet is recently examined. Preliminarily results are promising further investigations. In the present paper, authors have tried to check the feasibility of the SPIF process by establishing a comparative study between the composite bilayer sheet behavior low-carbon steel/commercially pure titanium (St/CP-Ti) in forming process and the forming behavior of a single layer sheet made of CP-Titanium. The effect of process parameters such as the vertical step size of the tool path, the initial sheet thickness and the wall angle inclination of a truncated pyramid were investigated with finite element method (FEM) approach on the forming forces and the thickness distributions. In other words, a numerical analysis is conducted in order to predict the forming forces and the homogeneity of the thickness variations of bilayer material compared to the single layer sheet. Finally, this study reveals the importance of the bilayer sheet as a low-cost material. In addition, it elucidates the flexibility of SPIF process to deform composite sheet.

Cold Rolling Reduction Dependence of the Recrystallization Texture of 3% Si Non-oriented Electrical Steel

The effect of the amount of cold reduction on the crystallographic texture, the microstructure, and the magnetic properties of cold rolled and annealed 3% Si non-oriented (NO) Si steel has been studied. The results indicate that, at constant final thickness, the combination of initial hot-rolled sheet thickness and the cold rolling reduction had a significant influence on the B50 magnetic flux density. The initial thickness of the hot-rolled sheet did not affect the crystallographic texture of the as-hot rolled sheet and the annealed hot-rolled sheet. At constant final thickness, the combination of a larger hot-rolled sheet thickness and a higher cold rolling reduction resulted in the decrease of the B50 magnetic flux density. This was due to an increase of the {411}<148> and {111}<112> texture components intensity and a decrease of the {110}<001> texture component intensity.

Approach for the Development of Forming Tools for Radial Rotation Profile-Forming

The incremental forming process Radial Rotation Profile-Forming (RRPF) has been developed to enable the production of profiled hollow parts with low sheet thinning and high geometrical accuracy. As a result of low thinning, a smaller initial sheet thickness can be used, while material and weight can be saved.The two principal forming steps are the production of the preform by Rotational Swing-Folding (RSB) and the subsequent radial profile forming of the hollow part in one clamping position. The special feature are the purposed wrinkles in the first process step, which formed in the indentation of the profiled mandrel. This is an advantage, because of the additional thickening. Due to the radial profiled forming in the second process step, the axial profile can be formed with less thinning.The focus of the article is on the development of the forming tools for the second process step of RRPF. Based on the general law of gearing, the forming tools for the production of a component are developed. First, a forming simulation of an example component validates the approach. For this purpose, some simplifications have been made in order to consider the profile forming process separately. Afterwards, the experimental results of the incremental sheet metal forming process for the production of the profiled hollow parts are presented.

Experimental and simulation studies on the mold replicability in the thermoforming process

Abstract In the precision thermoforming process, one of the main drawbacks occurs in the profile deviation of the produced part. In this study, the effect of different thermoforming process parameters on the mold replicability of a high impact polystyrene container produced by vacuum forming and drape forming processes has been experimentally and numerically investigated. According to experimental results, in the drape forming process, when the initial sheet thickness increases, the part will have higher mold replicability, whereas in the vacuum forming process, by increasing the initial sheet thickness, the mold replicability increases and reaches its peak, then decreases. The results also indicate that both temperature and vacuum pressure exhibit the most significant effect on mold replicability of the part. Furthermore, the finite element method is utilized by the implementation of a fully thermomechanically coupled hyperviscoelastic constitutive model in ABAQUS 6.13. By using this material model, it is possible to compare the sensitivity of the output (mold replicability of the part) to the changes in the range of the process parameters. The simulation results verified by the experimental data and the hyperviscoelastic model showed to be an outstanding and stable platform for the process simulation.